1. Field of the Invention
This invention relates to methods for generating monoclonal antibody against cell membrane proteins, and, more particularly, to methods for generating human monoclonal antibodies against cell surface coreceptors for human immunodeficiency virus (HIV) and using these antibodies for diagnostic or therapeutic purposes.
2. Description of Related Art
HIV infection has been implicated as the primary cause of the slowly degenerate disease of the immune system termed acquired immune deficiency syndrome (AIDS). Barre-Sinoussi et al. (1983) Science 220:868–870; and Gallo et al. (1984) Science 224:500–503. Infection of the CD4+ subclass of T-lymphocytes with the HIV-1 virus leads to depletion of this essential lymphocyte subclass which inevitably leads to opportunistic infections, neurological disease, neoplastic growth and eventually death. HIV-1 infection and HIV-1 associated diseases represent a major health problem and considerable attention is currently being directed towards the successful design of effective therapeutics.
HIV-1 is a member of the lentivirus family of retroviruses. Teich et al. (1984) In RNA Tumor Viruses ed. R. Weiss, N. Teich, H. Varmus, J. Coffin CSH Press, pp. 949–56. The life cycle of HIV-1 is characterized by a period of proviral latency followed by active replication of the virus. The primary cellular target for the infectious HIV-1 virus is the CD4 subset of human T-lymphocytes. Targeting of the virus to the CD4 subset of cells is due to the fact that the CD4 cell surface protein acts as the cellular receptor for the HIV-1 virus. Dalgleish et al. (1984) Nature 312:763–67; Klatzmann (1984) Nature 312:767–68; and Maddon et al. (1986) Cell 47:333–48.
After binding to the cell surface, the HIV-1 virion becomes internalized, and once inside the cell, the viral life cycle begins by conversion of the RNA genome into linear DNA molecules. This process is dependent on the action of the virally encoded reverse transcriptase. Following replication of the viral genome, the linear DNA molecule integrates into the host genome through the action of the viral integrase protein, thus establishing the proviral form of HIV-1.
It was later discovered that other than CD4, HIV-1 utilizes several cell membrane proteins as its coreceptor to falitate viral entry into the host cell. Alkhatib et al. (1996) Science 272: 1955–1958; and Deng et al. (1996) Nature 388:296–300. Examples of chemokine receptors include CXCR4, CCR5, CCR1, CCR2b, CCR3, CCR4, CCR8, CXCR1, CXCR2, CXCR3, and CX3CR1. Examples of chemokine receptor-like orphan proteins include STRL33/BONZO and GPR15/BOB.
CXCR4 (also known as “fusin”) is a receptor for chemokines such as SDF-1α and SDF-1β. CCR5 is a receptor for several CC chemokines such as MIP-1α (also named GOS19, LD78, pAT464 gene product, TY5 (murine) and SISα (murine)), MIP-1β (also named Act-2, G-26, pAT744 gene product, H-400 (murine) and hSISγ (murine)) and RANTES (regulated on activation, normal T cell expressed and secreted, or CCL5). Cocchi et al. (1995) Science 270:1811–1815; and Mellado et al. (2001) Annu. Rev. Immunol. 19:397–421. The roles of these CC chemokine molecules in regulating T cell fate include possible indirect effects on antigen-presenting cells and direct effects on differentiating T cells. Luther & Cyster (2001) Nat. Immunol. 2:102–107.
Specific chemokine receptors such as CXCR4 and CCR5 receptors play important roles in mediating HIV entry and tropism for different target cells. See reviews by Berger (1997) AIDS 11, Suppl. a: S3–S16; and Dimitrov (1997) Cell 91: 721–730; and Burger et al. (1999) Annu. Rev. Immunol. 17:657–700. Macrophages-tropic (M-tropic) strains of HIV virus can replicate in primary CD4+ T cells and macrophages and use the β-chemokine receptor CCR5 and less often, CCR3 receptor. T cell line-tropic (T-tropic) HIV strains can also replicate in primary CD4+ T cells but can in addition infect established CD4+ T cell lines in vitro via the α-chemokine receptor CXCR4. Many of the T-tropic strains can use CCR5 in addition to CXCR4. Chemokine receptor-like HIV coreceptor STRL33 is expressed in activated peripheral blood lymphocytes and T-cell lines and can function as an entry cofactor for Env proteins from M-tropic, T-tropic and dual tropic strains of HIV-1 and SIV. Other HIV coreceptors have also been identified by numerous in vitro assays, including chemokine receptors CCR2b, CCR3, CCR8 and CX3CR1 as well as several chemokine receptor-like orphan receptor proteins such as GPR15/BOB and STRL33/BONZO. Each or a set of these HIV coreceptors can mediate entry of different strains of HIV virus into the host cell.
The CC chemokine receptor CCR5 is a principal HIV-1 coreceptor that plays a dominant role in disease transmission and in the early course of infection. Berger et al. (1999) Annu. Rev. Immunol. 17:657–700. Molecular epidemiology studies clearly demonstrated that CCR5 plays critical roles in HIV-1 transmission and pathogenesis. Individuals lacking two copies of functional CCR5 alleles (Δ32 allele) are strongly protected against HIV-1 infection. Dean et al. (1996) Science 273:1856–1862. Individuals with one Δ32 and one normal CCR5 gene on average express lower levels of CCR5 on their T cells. Wu et al. (1997) J. Exp Med. 185:1681–1691. Heterozygosity for the Δ32 allele does not protect against HIV-1 infection but does confer an improved prognosis in the form of significantly increased AIDS-free and overall survival periods. Husman et al. (1997) Ann. Intern. Med. 127:882–890. Moreover, CCR5 heterozygotes are overrepresented among long-term nonprogressors, i.e., those individuals who do not progress to AIDS after 10 or more years of infection. Dean et al. (1996) Science 273:1856–1862. Because it is an essential coreceptor for clinically relevant strains of HIV-1 and yet is apparently dispensable for human health, CCR5 provides an attractive target for new antiretroviral therapies. Liu et al. (1996) Cell 86:367–377; and Michael & Moore (1999) Nat. Med. 5:740–742.
Several approaches have been employed to target HIV coreceptors, involving proteins, peptides and small molecules. It has been found that some CCR5-targeting chemokines and chemokine analogs are capable of inhibiting HIV-1 replication in vitro. Berger et al. (1999) Annu. Rev. Immunol. 17:657–700. Of the CC chemokines that bind CCR5, RANTES possesses significantly greater breadth of antiviral activity than MIP-1α and MIP-1β, although all CC chemokines show interisolate variation in potency. Trkola et al. (1998) J. Viol. 72:396–404. The antiviral activity of the CC chemokines better correlates with their ability to downregulate rather than to bind CCR5 on CD4 T cells, and sustained down-regulation of CCR5 has been suggested to be a principal mechanism of action for the chemokine analog aminooxypentane (AOP)-RANTES. Mack et al. (1998) J. Exp. Med. 187:1215–1224. A small non-peptide molecule designated TAK-779 was found to be an antagonist against CCR5 presumably through binding to a hydrophobic pocket defined by the transmembrane helices 1, 2, 3 and 7. Baba et al. (1999) Proc. Natl. Acad. Sci. USA 96:5698–5703; Shiraishi et al. (2000) J. Med. Chem. 43:2049–2063; and Dragic et al. (2000) Proc. Natl. Acad. Sci. USA 97:5639–5644.
Phage display has been utilized to select for single chain antibody against CCR5 from a human antibody library by using CCR5-expressing CD4+ lymphocytes as the target in the presence and absence of MIP-1α. Osbourn et al. (1998) Nature Biotech. 16:778–781. The selected phage particles were analyzed by phage ELISA for their ability to recognize CD4+ lymphocytes, CCR5-transfected CHO cell line, non-transfected CHO cell line, and a BSA-conjugated peptide corresponding to the N-terminal 20 amino acid peptide of CCR5. Osbourn et al. found that none of the antibodies selected in the presence of MIP-1α blocked MIP-1α binding to CD4+ lymphocytes. Among the antibodies selected in the absence of MIP-1α, around 20% inhibited MIP-1α binding to CD4+ lymphocytes, as well as MIP-1α-mediated calcium signaling.
Mouse monoclonal antibodies have also been generated to target CCR5 by using the whole protein of CCR5 as the antigen. For example, Wu et al. immunized mice with the murine pre-B cell lymphoma cell line L1.2 expressing high levels of transfected CCR5, which generated a IgG1 monoclonal antibody, designated as mAb 2D7. Wu et al. (1997) J. Exp. Med. 186:1373–1381. The binding site of this monoclonal on CCR5 was mapped to the second extracellular loop of CCR5. MAb 2D7 was shown to be able block the binding and chemotaxis of the three natural chemokine ligands of CCR5, RANTES, macrophage inflammatory protein MIP-1α, and MIP-1β, to CCR5 transfectants. MAb 2D7 failed to stimulate an increase in intracellular calcium concentration in the CCR5 transfectants, but blocked calcium response elicited by RANTES, MIP-1α and MIP-1β chemotactic responses of activated T cells, but not of monocyte. In contrast, a group of mAbs that were also generated in the same process and failed to clock chemokine binding were all mapped to the N-terminal region of CCR5.
Using a similar strategy to Wu et al. (1997), Olson et al. isolated 6 anti-CCR5 murine monoclonal antibodies (MAbs) by intraperitoneally immunizing female BALB/c mice with murine L1.2 cells expressing CCR5. Olson et al. (1999) J. Virol. 73:4145–4155. Epitope mapping of these MAbs reveals that the epitopes of these antibodies reside in the N-terminus and/or second extracellular loop regions of CCR5. This structural information was correlated with the antibodies' abilities to inhibit (1) HIV-1 entry; (2) HIV-1 envelope glycoprotein-mediated membrane fusion; (3) gp120 binding to CCR5; and (4) CC-chemokine acitvity. Surprisingly, each of the antibodies displayed distinctly different activities in different stages of HIV-1 entry. In particular, one of these MAbs, PRO140, was shown to exert inhibitory effects on HIV-1 infection on primary peripheral blood mononuclear cells (PBMC). Trkola et al. (2001) J. Virol, 75:579–588.